Answer by Viola Yee,
A quick and easy way is to add a spoonful of minute tapioca along with the apple slices and toss it all in a bowl with the sugar and spices. Then pile the slices in the crust. The tapioca soaks up the excess apple juice and turns it into a soft jelly. This gives the characteristic texture of pies that you get from commercial bakeries. I personally don't like that texture in apple pie, but I do use tapioca for Cherry Pies.
Your problem might be that you are using very watery apples to start with. I use Spartans when I can get them, and I don't have a problem with watery pies. Granny Smith, Honey Crisp, Cox's Orange Pippin, and Northern Spy are also preferred for pies because they are drier than the eating-out-of-hand apples. These firm Baking or Pie apple types hold their shape and flavor during cooking.
Eating apples (aka Dessert apples), including the ubiquitous Red Delicious and Gala types, are not good for pies because they are watery and cook down into mush.
See also: Baking: What are the best kinds of apples to use in a homemade apple pie?
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